This invention relates generally to telemetry systems for physiological implants and more particularly, it relates to a telemetry system for communicating with an implanted cardiac pacer which samples each drive current pulse applied to a telemetry tank for recovering telemetered data from the pacer.
Heretofore, there have been proposed in the prior art verious telemetry systems for transmitting data into an implanted cardiac pacer as well as systems for signalling out data from the implanted pacer. However, one problem encountered in these prior art systems is that the telemetry reception rate from the pacer could not exceed 4k baud due to the carrier noise in the data recovery circuitry and to the limitation of the bandwidth of the telemetry coil. Another problem experienced in the prior art telemetry systems is that they use a standard active, low pass filter which limited the data recovery rate.
It would therefore be desirable to provide an improved telemetry system for recovering data from an implanted pacer at data rates in excess of 4k baud, but eliminates any carrier noise in the data recovered. The telemetry system of the present invention utilizes a pair of sample and hold circuits connected in series functioning as a clocked filter for sampling of each drive current pulse applied to a telemetry tank. Any change in the electromagnetic field generated by the current pulses as affected by the pacer will be reflectd in changes in the drive current pulses. Thus, by sampling such current pulses telemetered data from the pacer may be recovered from these sampled values.